Method and apparatus for testing using a transceiver module

ABSTRACT

An apparatus in one embodiment includes a transceiver housing operable to be inserted into a port of a host system, the port comprising at least a first channel and a second channel. The transceiver housing may be a compact small form-factor (SFP) pluggable module housing. The apparatus also includes a printed circuit board mounted in the transceiver housing and an electrical interface of the printed circuit board operable to interface with the port of the host system. The electrical interface includes a first transmit pin and a first receive pin configured to interface with the first channel of the port and a second transmit pin and a second receive pin configured to interface with the second channel of the port. A first connector couples the first transmit pin and the second receive pin, and a second connector couples the second transmit pin and the first receive pin.

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to communication systems and moreparticularly to a method and apparatus for testing a communicationsystem using a transceiver module.

BACKGROUND OF THE INVENTION

Modern mixed communications networks employ various transceiver modulesto interface between disparate network types. For example, compact smallform-factor pluggable (SFP) transceiver modules are transceivers used tocouple fiber optic and electronic host systems and/or networks. CompactSFP modules are designed to be inserted into a port of a host systemwith an electrical interface. In turn, compact SFP modules providereceptacles for fiber optic cables with a fiber optic interface. CompactSFP modules convert electrical signals received from the host system tooptical signals transmitted over the fiber optic network. Compact SFPmodules also convert optical signals transmitted over the fiber opticnetwork to electrical signals transmitted to the host system. Hostsystems and devices in such networks often require that testing andverification procedures be successfully completed before they arereleased and/or introduced into a communications network. Testing andverification of those systems and devices, however, has proven costlyand inefficient.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsadvantages, reference is now made to the following description, taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating an example communication system;

FIG. 2 is a block diagram illustrating an example embodiment oftransceiver module for testing a communications system; and

FIG. 3 is a chart illustrating the pin assignment for an electricalinterface to a compact SFP module; and

FIG. 4 is a flowchart illustrating an example method for testing acommunication system using a transceiver module.

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE

Overview

The teachings of the present disclosure relate to an apparatus thatincludes a transceiver housing operable to be inserted into a port of ahost system, the port comprising at least a first channel and a secondchannel. The transceiver housing may be a compact small form-factor(SFP) pluggable module housing. The apparatus also includes a printedcircuit board mounted in the transceiver housing and an electricalinterface of the printed circuit board operable to interface with theport of the host system. The electrical interface includes a firsttransmit pin and a first receive pin configured to interface with thefirst channel of the port and a second transmit pin and a second receivepin configured to interface with the second channel of the port. A firstconnector couples the first transmit pin and the second receive pin, anda second connector couples the second transmit pin and the first receivepin.

Description

FIG. 1 is a block diagram illustrating an example communication system10. Communication system 10 includes a host system 20, which may formall or a part of a copper network 30. Host system 20 may be connected toa fiber network 32 via a transceiver 40. Host system may include anumber of ports 22 that have a receptacle configured to couple anelectrical interface of transceiver 40 to a corresponding electricalinterface 24 of port 22. Transceiver 40 may be coupled to fiber opticnetwork 32 via fiber connection 42 and may be seated in the receptacleof port 22. In general, host system 20 transmits and receives data overcopper network and/or fiber network 32. Transceiver 40 providesconnectivity between copper network 30 and fiber optic network 32.Transceiver 40 receives electronic signals from electrical interface 24of host system 20, converts those signals into optical signals, andtransmits the optical signals to fiber optic network 32. Transceiver 40also receives optical signals from fiber optic network 32, convertsthose signals into electronic signals, and transmits the electronicsignals to host system 20 via electrical interface 24.

Host system 20 represents a switch, router, gateway, hub, or othernetwork device configured to send and receive data. Host system 20 maysend and receive data over copper network 30 and may interface withtransceiver 40 in order to transmit and receive data from fiber network32. Host system 20 may include a number of ports 22 configured toreceive transceivers 40. Ports 22 may support two or more duplexconnections to transceiver 40. Each of ports 22 may have a receptacleconfigured to allow electrical interface of transceiver 40 to interfacewith an electrical interface 24 of host system 20. For example, port 22may be configured to guide a compact SFP transceiver 40 into areceptacle to interface with electrical interface 24. In suchembodiments, electrical interface 24 may represent a 20-pin connectorcompatible with compact SFP transceivers. The pin assignment of anexample compact SFP interface is illustrated in FIG. 3. Host system 20may communicate with copper network 30 and/or fiber network 32 using anynumber and combination of network protocols such as Ethernet, Fiberchannel, and/or other network protocols.

Copper network 30 is a network with at least some copper links and maycomprise any number of devices and connections used to support any of avariety of protocols and features. For example, copper network 30 mayrepresent one or more Ethernet or gigabit Ethernet networks. Fibernetwork 32 is a network with at least some fiber links and may compriseany number of devices and connections used to support any of a varietyof communications protocols and features. For example, fiber network 32may comprise one or more SDH or fiber channel networks. The term networkshould be interpreted as generally defining any interconnection ofcomponents capable of transmitting audio and/or video communicationssignals, data, messages and other information including signals, data ormessages transmitted through streaming media, text, chat, instantmessaging, and/or email. Networks described herein may be implemented asor be connected to one or more of a local area network (LAN), a widearea network (WAN), a public switch telephone network (PSTN), and/or aglobal distributing network such as the Internet, intranet, extranet, orother form of wireless or wireline communication network and may be acombination of network types such as those listed above. Any networkcomponents capable of changing an audio, video or other data usingfriends or packets are included within the scope of particularcomponents.

Transceiver 40 represents a device operable to facilitate communicationsbetween copper network 30 and fiber network 32. Each transceiver 40 maybe capable of establishing two or more duplex connections between coppernetwork 30 and fiber network 32. Transceiver 40 may, for example, be acompact SFP transceiver capable of duplex fiber connections to fibernetwork 32. Transceiver 40 converts optical signals to electricalsignals and converts electrical signals to optical signals. Accordingly,transceiver 40 may receive optical signals from fiber network 32,convert those optical signals into electronic signals and transmit theelectronic signals to electrical interface 24 of host system 20.Transceiver 40 may receive electronic signals from host system 20,convert those electronic signals into optical signals and transmit theoptical signals to fiber network 50. Transceiver 40 may be inserted intoa corresponding receptacle of port 22 in host system 20. In certainembodiments, inserting transceiver 40 into the receptacle results in aconnection between an electrical interface of transceiver 40 andcorresponding portions of electrical interface 24. For example, acompact SFP transceiver 40 may include an electrical interface operableto interface with a 20-pin connector of host system 20. Becausetransceiver 40 may be capable of transmitting data and receiving dataover two or more channels, transceiver 40 may be capable of establishingtwo or more optical connections to fiber network 50.

As discussed above, transceiver 40 and host system may interface usingelectrical interface 24. In certain embodiments, host system 20 includeselectrical interface 24 that has a 20-pin connector, and transceiver 40has an electrical interface capable of coupling with the 20-pinconnector. For example, each portion of the 20-pin connector mayinterface with a corresponding pin on transceiver 40. A portion of the20-pin connector may include pins for transmitting and receiving data oneach channel of transceiver 40. For example, transceiver 40 may includetwo channels, with channel 1 including TX+/− pins and RX+/− pins andwith channel 2 including TX+/− pins and RX+/−. Other pins of the 20-pinconnector may correspond to other functionality appropriate fortransceiver 40. An example pin assignment for a compact SFP transceiver40 is described below with respect to FIG. 3.

Deviations in manufacturing tolerances, component quality, and othercircumstances may introduce errors into communications system 20.Accordingly, various components of communication system 10 may requiretesting to prevent and/or correct such errors prior to sale and/ordeployment in a production network environment. For example, host system20 may be tested before being deployed into communications system 10.Accordingly, testing may be required to ensure that host system 20 willfunction correctly when introduced into communications system 10.Operational, burn-in, de-bugging, troubleshooting, or other testing maybe employed to ensure that host system 20 operates in the intendedmanner. Such testing may require the use of fiber optic cabling 42 andthe use of multiple transceivers 40. For example, two ports 22 of hostsystem 20 may be tested using two transceivers 40 and a fiber opticcable 42. The first port 22 may be coupled to the second port 22 usingfiber optic cable 42. Such components are often expensive and/orunreliable. For example, fiber optic cable 42 may be subject to frequentfailure. As explained below with respect to FIG. 2, however, transceiver60 may be employed to test host system 20 without the use of fibercabling 42 or transceivers 40.

FIG. 2 is a block diagram illustrating an example embodiment of atransceiver module 60 for testing communications system 10. In general,transceiver 60 may facilitate testing of host system 20. In particular,transceiver module 60 represents a device operable to facilitate testingof at least two channels of port 22 in host system 20. Transceiver 60may facilitate loop-back testing of the physical channels of port 22.

Transceiver 60 includes a housing 62 and a printed circuit board 64 thatmay have an electrical interface 66 and feedback circuit 66. Printedcircuit board 64 may be mounted in housing 62. In some embodiments,transceiver module 60 may include identification module 76 and/orauthentication module 78. In some embodiments, housing 62 may representa compact SFP housing. Housing 62 may be operable to be inserted intoreceptacle of port 22 in a similar manner as was described above withrespect to transceiver 40.

Printed circuit board 64 represents one, or more substrates havingelectronic trace connectors. Printed circuit board 64 supports and/orcouples the various electrical components of transceiver 60. Printedcircuit board 64 may include an electrical interface 66 and feedbackcircuit 68. Electrical interface 66 may be operable to interface withelectrical interface 24 of host system 20. Electrical interface 66 may,for example, represent a 20-pin connector. Accordingly, electricalinterface 66 may include pins operable to interface with duplex channelsassociated with compact SFP transceivers. In the case where transceivermodule has a compact SFP housing, the pin assignment of electricalinterface 66 may correspond to that described below with respect to FIG.3.

Feedback circuit 68 may include electrical trace connectors 70 and 72.Trace connectors 70 and 72 may couple the channels of port 22 to eachother in pairs. Trace connectors 70 and 72 are operable to couple thetransmit pins of channel 1 to the receive pins of channel 2 and thereceive pins of channel 1 to the transmit pins of channel 2.

Trace connector 70 may include a pair of connectors 70 a and 70 b.Likewise, trace connector 72 may include a pair of connectors 72 a and72 b. As illustrated, trace connector 70 a may couple the TX− pin ofchannel 1 to the RX− pin of channel 2, and trace connector 70 b maycouple the TX+ pin of channel 1 to the RX+ pin of channel 2. Similarly,trace connector 72 a may couple the TX− pin of channel 2 to the RX− pinof channel 1, and trace connector 72 b may couple the TX+ pin of channel2 to the RX+ pin of channel 1. In some embodiments, each of connectors70 a and 70 b and connectors 72 a and 72 b may respectively include acapacitor. Each capacitor C1, C2, C3, and C4 may be of any capacitancesuitable to remove DC components of signals transmitted by channels 1and 2 of port 22. For example, each capacitor may be a 0.01 microfaradcapacitor, 0.10 microfarad capacitor, or have other appropriatecapacitance. Removing such DC components using capacitors may facilitatehigh speed data transmission rates. In some embodiments, the TX− pin ofchannel 2 may also be coupled to ground by a resistor R1. R1 may be ofany appropriate resistance. For example, R1 may be approximately 500ohms. R1 may facilitate compatibility of transceiver 60 with bothcompact SFP and SFP ports 22 of host system 20.

Using feedback circuit 68, printed circuit board 64 may be operable toreceive information from channel 1 of port 22 and transmit thatinformation to channel 2 of port 22. Printed circuit board 64 may alsoreceive information from channel 2 of port 22 and transmit thatinformation to channel 1 of port 22. It should be understood, however,that while an example embodiment of transceiver 60 is illustrated, theteachings of the present disclosure are intended to encompassembodiments of host system 20 having more than two channels per port. Insuch embodiments, an additional trace connector may be provided for eachadditional pair of channels.

In some embodiments, trace connectors 70 and 72 may be capable ofsimulating the signal attenuation and/or losses associated withtransmission lines in fiber network 32. Within fiber network 32, signalattenuation may be associated with, for example, the length, quality,and/or other characteristics of fiber optic cables 42 and/or othercomponents of fiber network 32. To simulate such signal attenuation,trace connectors 70 and 72 may utilize areas of printed circuit board 64to form a pattern, which may lengthen the trace of the connectors andmay increase the corresponding signal attenuation. Trace connectors 70and 72 may in some embodiments be operable to simulate a signalattenuation between 0 decibel and 20 decibels. As another example, traceconnectors 70 and 72 may use different materials capable of simulatingthe loss. In some embodiments, trace connectors 70 and 72 may beconnected to microchip attenuators operable to achieve a similar result.

Identification module 76 represents any combination of hardware,software, and controlling logic operable to identify transceiver 60 tohost system 20. In the illustrated embodiment, identification module 76may include an electrically erasable programmable read-only memory(EEPROM). Identification module 76 may be coupled to appropriate pins ofelectrical interface 66. In some embodiments, authentication module 76may be mounted on printed circuit board 64. In response to a requestfrom host system 20, identification module 76 may transmit informationidentifying transceiver 60 to host system 20. For example,identification module 76 may transmit information indicating thattransceiver module 60 is a testing module. Alternatively or in addition,identification module 76 may transmit information indicating thattransceiver module 60 is a transceiver 40, such as a compact SFPtransceiver. In some embodiments, identification module 76 may becapable of identifying the basic function of transceiver module 60 tohost system 20. For example, identification module 76 may identify thattransceiver module 60 is a test module for use in testing. In otherembodiments, identification module 76 may transmit information to hostsystem 20 indicating that transceiver 60 is connected to fiber network32 even transceiver module 60 it is not actually connected to fibernetwork 32. Accordingly, identification module 76 may be capable ofresponding to a request for identification received from host system 20over electrical interface 24 and electrical interface 66 in any suitablemanner that may be expected by host system 20.

Authentication module 78 represents any combination of hardware,software, and controlling logic operable to transmit a cryptographicauthentication signature to host system 20. For example, host system 20may be capable of authenticating transceiver module 60 using a publickey authentication (PKA) scheme. Authentication module 78 may be capableof responding to an authentication request via host system 20 byproviding information digitally signed with a private key to host system20. If the private key signature corresponds to a public key on a listof trusted entities stored on host system 20, host system 20 mayauthenticate transceiver module 60. It should be understood that while aparticular method of authentication has been described, the principlesof the present disclosure apply to any number and types ofauthentication schemes.

In operation, transceiver module 60 facilitates testing of host system20. Transceiver module 60 may be inserted into port 22 in a testingenvironment. Host system 20 may begin a procedure to initiatetransceiver module 60. The procedure may, in some embodiments, be thesame procedure host system 20 may use to initiate transceiver 40. Forexample, host system 20 may request transceiver module 60 to identifyitself. Alternatively or in addition, host system 20 may initiate anauthentication procedure in which host system 20 determines iftransceiver module 60 is a trusted device. After receiving aidentification and/or authentication response from transceiver 60, hostsystem 20 may determine whether the identification and/or authenticationis valid. If so, host system 20 may allow data to be transmitted and/orreceived on the channels of port 22 as if port 22 were connected tofiber network 32. In some embodiments, host system 20 may interact withtransceiver 60 in a same or similar manner as it would interact withtransceiver 40.

Host system 20 may transmit data and receive data over the variouschannels of port 22. Accordingly, transceiver 60 may simulate thecharacteristics of fiber network 32 to host system 20. For example,transceiver 60 may receive information on channel 1 and transmit thatinformation to channel 2, and may receive information on channel 2 andmay transmit that information to channel 1. If the informationtransmitted on one channel is confirmed as received on the other, theability for host system 20 to correctly send and receive data may beconfirmed. Alternatively or in addition, other testing procedures may beemployed to test and/or simulate various aspects of host system 20.

FIG. 3 is a chart 300 illustrating an example pin assignment for a20-pin electrical interface 66 to a transceiver 60. In particular, chart300 may correspond to the pin assignment for a compact SFP transceiver.Thus, a transceiver 60 having a compact SFP transceiver housing maycouple to port 22 of host system 20 using the pin assignment describedin chart 300.

Chart 300 includes pin assignments for channels 1 and 2 of a compact SFPtransceiver operable to be inserted into port 22 of host system 20. Inparticular, pins 18 (TD+1) and 19 (TD−1) may correspond to the transmit(TX+/−) pins of channel 1, while pins 12 (RD−1) and 13 (RD+1) maycorrespond to the receive (RX+/−) pins of channel 1. Pins 6 (TD−2) and 7(TD+2) correspond to the transmit (TX+/−) pins of channel 2. Pins 9(RD+2) and 10 (RD−2) correspond to the receive (RX+/−) pins of channel2. In some embodiments, pins 3 and 17 may correspond to transmissiondisable pins. Transceiver 60 module may include appropriate circuitryoperable to enable those pins while transceiver 60 is coupled to port 22of host station 20. Enabling the transmission disable pins may allowtransceiver 60 to provide continuous transmissions during testing.

As described above, feedback circuit 68 may include trace connectors 70and 72 to couple channel 1 to channel 2. In some embodiments, traceconnector 70 a may couple pin 19 (TD−1) to pin 10 (RD−2), and traceconnector 70 b may couple pin 18 (TD+1) to pin 9 (RD+2). Accordingly,trace connector 72 a may couple pin 6 (TD−2) to pin 12 (RD−1), and traceconnector 72 b may couple pin 7 (TD+2) to pin 13 (RD+1). Transceiver 60may also include appropriate electrical connections to coupleidentification module 68 and/or authentication module 70 to electricalinterface 66 as represented by chart 300 in FIG. 3.

FIG. 4 is a flow chart illustrating an example method of testing acommunication system 20 using transceiver module 60. At step 402,transceiver module 60 is inserted in at least a two channel port 22 ofhost system 20. Host system 20 may, in turn, attempt to initiatetransceiver 60 at step 404. For example, this step may includetransmitting a identification request to identification module 76 overthe appropriate pins of electrical interfaces 24 and 66. In response tothe identification request, identification module 76 may transmitidentifying information to host system 20. In some embodiments,identification module 76 may also identify its purpose to host system20. In other embodiments, identification module 76 may transmitinformation to host system 20 indicating that transceiver module 60 iscoupled to fiber network 32 even if it is not.

At step 406, once host system 20 receives the identifying information,host system 20 determines if transceiver 60's identity is recognized. Ifthe identity is not recognized, host system 20 may at step 408 disableport 22. In some embodiments, host system 20 may return and/or indicatean error condition. If the identity is recognized, then the identity oftransceiver 60 is approved. At step 410, the host system 20 may requestan authentication signature. Once authentication module 78 transmits adigital signature, the signature is authenticated at step 412. If thedigital signature is not authenticated then the method may return tostep 408.

If transceiver 60 is authenticated, however, then at step 414 hostsystem 20 will receive an active network signal from identity module 76of transceiver module 60. Accordingly, host system 20 may treattransceiver module 60 as if it is connected to fiber network 32. In someembodiments, transceiver module 60 is not connected to fiber network 32,but is merely providing a feedback circuit between the channels of port22. Regardless, host system 20 may not know that port 22 is notconnected to fiber network 32.

At step 416, a testing procedure may be initiated. A testing proceduremay include transmitting information on channel 1 at step 418 and thendetermining whether information was received on channel 2 at step 420.If the information was not received, then the testing procedure maydetermine whether a time-out was reached at step 422. If a time out hasbeen reached then the method may proceed to step 424, where the testingprocedure may be failed. If at step 422 the time out has not beenreached, then the testing procedure may return to step 420. If theinformation has been received at step 420 then the testing procedurecontinues to step 426.

At step 426, information is transmitted on channel 2. At step 430, adetermination is made as to whether the information transmitted onchannel 2 was received on channel 1. If the information was notreceived, then the testing procedure may determine whether a time-outwas reached at step 428. If a time out has been reached then the methodmay proceed to step 424, where the testing procedure may be failed. Ifat step 428 the time out has not been reached, then the testingprocedure may return to step 430. If the information has been receivedat step 430 then the testing procedure continues to step 432 and thetest completes.

Using the teachings of the present disclosure various transceivermodules 60 may simultaneously and/or sequentially test each port 22 inhost system 20. Because the need for expensive cabling has beeneliminated the testing procedure is much more streamline and efficientand all is right with the world.

It should be noted that while the method 400 illustrates the first andsecond channels as being tested sequentially, the method is fullyintended to allow various ports 22 of host system 20 to be testedsimultaneously using various transceivers 60. The steps illustrated byFIG. 4 as happening sequentially are for the purpose of illustrationonly. In addition, modifications, additions, or omissions may be made tomethod 400 illustrated in the flowchart of FIG. 6. For example, method400 may test ports 22 having more than two channels. In addition, thetest procedure described is only an example of a testing procedure thatmay be used and the teachings of the present disclosure are intended toencompass any number and types of tests that may be appropriate to testthe functionality of host system 20 using transceiver 60, includingburn-in and other forms of testing. Additionally, the steps of FIG. 4may be performed in parallel or in any suitable order.

Although the present invention has been described with severalembodiments, a myriad of changes, variations, alterations,transformations, and modifications may be suggested to one skilled inthe art, and it is intended that the present invention encompass suchchanges, variations, alterations, transformations, and modifications asfall within the scope of the appended claims.

1. An apparatus comprising: a transceiver housing operable to beinserted into a port of a host system, the port comprising at least afirst channel and a second channel; a printed circuit board mounted inthe transceiver housing; an electrical interface of the printed circuitboard operable to interface with the port of the host system, theelectrical interface comprising: a first transmit pin and a firstreceive pin configured to interface with the first channel of the port;a second transmit pin and a second receive pin configured to interfacewith the second channel of the port; a first connector coupling thefirst transmit pin and the second receive pin; and a second connectorcoupling the second transmit pin and the first receive pin.
 2. Theapparatus of claim 1, wherein the transceiver housing comprises acompact small form-factor (SFP) pluggable module housing.
 3. Theapparatus of claim 1, further comprising an identification modulemounted on the printed circuit board, the identification module operableto identify the apparatus to the host system.
 4. The apparatus of claim2, wherein the identification module is further operable, during testingof the host system, to indicate to the host system that the apparatus isconnected to a network even if the apparatus is not connected to anetwork.
 5. The apparatus of claim 1, further comprising: anauthentication module mounted on the printed circuit board, theauthentication module operable to transmit an authentication signatureto the host system.
 6. The apparatus of claim 1, wherein the firstconnection and the second connection are operable to simulate lossesassociated with fiber optic transmission lines.
 7. An apparatuscomprising: a compact SFP transceiver housing operable to be insertedinto a receptacle in a host system, the receptacle providing aninterface to a first channel and a second channel; a printed circuitboard mounted to the compact SFP transceiver housing, the printedcircuit board having traces to couple the first channel to the secondchannel, wherein the printed circuit board is operable to: receive firstinformation on the first channel and transmit said first information tothe second channel; and receive second information on the second channeland transmit said second information to the first channel.
 8. Theapparatus of claim 7, further comprising an identification modulemounted on the printed circuit board, the identification module operableto identify the apparatus to the host system.
 9. The apparatus of claim8, wherein the identification module is further operable, during testingof the host system, to indicate to the host system that the apparatus isconnected to a network even if the apparatus is not connected to anetwork.
 10. The apparatus of claim 7, further comprising: anauthentication module mounted on the printed circuit board, theauthentication module operable to transmit an authentication signatureto the host system.
 11. The apparatus of claim 7, wherein the firstconnection and the second connection are operable to simulate lossesassociated with fiber optic transmission lines.
 12. A method comprising:initiating a transceiver module connected to a port of a host system,the port comprising at least a first channel and a second channel, andthe transceiver module comprising a printed circuit board having tracesto couple the first channel to the second channel; transmitting firstinformation on the first channel; determining that the first informationis received on the second channel; transmitting second information onthe second channel; and determining that the second information isreceived on the first channel.
 13. The method of claim 13, wherein thetransceiver module further comprises a compact small form-factor (SFP)pluggable module housing and the printed circuit board is mounted to thecompact SFP module housing.
 14. The method of claim 12, furthercomprising: querying an identification module in the transceiver module;and determining the identity of the transceiver module.
 15. The methodof claim 14, further comprising: receiving, during testing of the hostsystem, an indication that the transceiver module is connected to thenetwork even if the transceiver module is not connected to a network.16. The method of claim 12, further comprising: requesting that thetransceiver module transmit an authentication signature to the hostsystem; receiving the authentication signature from the transceivermodule; and authenticating the transceiver module.
 17. A systemcomprising: a host system, the host system comprising a port thatincludes at least a first channel and a second channel; and atransceiver module, the transceiver module comprising: a compact SFPtransceiver housing operable to be inserted into the port in the hostsystem; a printed circuit board mounted to the compact SFP transceiverhousing, the printed circuit board having traces to couple the firstchannel to the second channel, wherein the printed circuit board isoperable to: receive information on the first channel and transmit saidinformation to the second channel; and receive information on the secondchannel and transmit said information to the first channel.
 18. Thesystem of claim 17, the transceiver module further comprising anidentification module mounted on the printed circuit board, theidentification module operable to identify the transceiver module to thehost system.
 19. The apparatus of claim 18, wherein the identificationmodule is further operable, during testing of the host system, toindicate to the host system that the transceiver module is connected toa network even if the apparatus is not connected to a network.
 20. Theapparatus of claim 17, wherein the first connection and the secondconnection are operable to simulate losses associated with fiber optictransmission lines.